Fasting Endurance and the Evolution of Mammalian Body Size

The idea that the need for energy reserves may have been important in the evolution of different body sizes can be traced to Lindsey (1966) who recognized that 'the energy reserves may last longer in large rather than in small animals' and suggested that this may be one possible reason for large body sizes among northern poikilotherms. Several subsequent investigators drew similar conclusions based on studies of other taxonomic groups. A number of environmental correlates of body size among mammalian carnivores suggested that 'homeostatic needs' might set a lower limit to body size at higher latitudes (Rosenzweig, 1968). Body size in whales is inversely correlated with the length of the feeding season and suggests that large size reflects the need for energy reserves during the fasting period (Brodie, 1975). Large body size has also been recognized as important in enhancing the survival of terrestrial vertebrates during periods of resource shortage in strongly seasonal environments (Boyce, 1979; Murphy, 1985; Zeveloff Calder, 1974, 1984; Searcy, 1980, Peters, 1983; Lindstedt Ralls, 1976; but see Shine, 1988). Despite this diverse support over many years, energy reserves and fasting endurance are not commonly incorporated into models considering the evolution of mammalian body size. Most